Voice onset time (VOT)
• Primary cue for distinguishing voiced and
voiceless stop consonants
• Delay between release and vocal fold
vibration
• Much longer in voiceless stops
– 0 - 20 ms = voiced
– 40 - 100 ms = voiceless
English speakers
Source: Lisker & Abramson, 1964
Thai speakers
Source: Lisker & Abramson, 1964
1
Categorical Perception
• Continuum from blue to green
• Continuum from /g/ to /k/
– VOT ranging from 0 ms to 80 ms in steps
Identification/rating task
• Label each item as being a member of one
category or the other
• Sometimes add in “goodness rating”
• For example, a 6-item rating going from a
good clear blue (1) to a good clear green (6)
– 2 = mostly blue
– 3 = borderline, but more blue than green
– 4 = borderline, but more green than blue
– 5 = mostly green
Color identification/rating results
6 B B
B
B
Average rating; 6 = blue, 1 = green
5
B
4 B
B
3 B
B
2 B
B B
1 B B
Series members
2
Speech identification/rating
results
6 B B B B
B
Average rating; 6 = voiced, 1 = voiceless
5 B
B
3
2 B
1 B B B B B
Series members
Discrimination tasks
• AX
• ABX
– 1 step: 1-2-2, 4-3-3, 7-8-7, 6-5-6
– 2 step: 1-3-3, 4-2-2, 6-8-6, 7-5-7
Color discrimination results
100 B B B
90 B B B
B B B
80 B B B
Discrimination accuracy
70
60
50
40
30
20
10
0
Series members
3
Speech discrimination results
100 B
90
80
Discrimination accuracy
70
B B
60
B B B B B
50 B B B B
40
30
20
10
0
Pairs of adjacent series members
Categorical Perception
• As if people can only perceive category
information
• Found for many different consonant
distinctions
• Not found for vowels
Differences among items that fall into different
categories are exaggerated, and differences among items
that fall into the same category are minimized.
Source: cognitrn.psych.indiana.edu/rgoldsto/projects/categorical.html
4
Example stimuli
• Series 1
• Series 2
• Series 3
• Series 4
• Same/different task
Same-Different Answers
1. Different 11. Same
2. Same 12. Different
3. Different 13. Different
4. Same 14. Different
5. Same 15. Different
6. Different 16. Different
7. Different 17. Same
8. Same 18. Different
9. Different 19. Different
10. Same 20. Different
Same-Different Answers, cont.
• Compare your results across the continuum:
– /g/ end of the continuum = numbers 1, 2, 7, 8,
10, 13, 16, 20
– /k/ end of the continuum = numbers 3, 4, 11, 12,
14, 18
– Middle of the continuum = numbers 5, 6, 9, 15,
17, 19
5
Consonant results
Vowel results
Interpretations
• Is speech special?
6
Animals show categorical
perception
• Pat Kuhl trained chinchillas to label
endpoints of a speech continuum
• Tested on other members of series
Chinchilla results
• Chinchillas showed the same categories,
although slightly less steep
Source: Kuhl, 1975
Chinchilla results, cont.
Source: Kuhl & Miller, 1978
7
Who cares about categorical
perception?
• Because phonemes are heard categorically,
distinctions that do not occur in your
language are not heard, even though they
may occur in other languages.
• This poses a problem for second language
learning & accent reduction.
